If you are a mechanical designer reading this, you should realize that you may have more influence over the cost of the final solution than any other person in the entire value chain. That's because you determine the roadmap for everyone else. Yes, whether an assembler can wire a station in 50 hours versus 60 obviously affects the bottom line profits, but you determine what needs wired in the first place by your concept, your choice of solution, and the components you select. I tend to view it that you set the base cost curve by the design you pursue and everyone else's performance (yours included) can only be variation (positive and negative) around that curve. Which brings me to the title of the post. It is a somewhat common scene to observe a project manager and a designer brainstorming a concept or reviewing a partially completed design and have one of them say they are worried about the part moving in the nest and the other to reply "We could clamp it. It's only a $100 cylinder, let's put it in to be safe." Of course, they know that cylinder doesn't just hang in space and work on its own for $100, so they are exaggerating, but I think people do tend to underestimate the total cost of implementing a motion. Let's take my example and expand it. Because it's only a simple clamp, let's choose a $100 ISO standard cylinder like the picture, screw some hardened tooling directly to the rod, and mount it to a simple right angle weldment from the base (not great design principles at play in my example, but that's a subject for another post. This is just meant to illustrate a point). Now let's throw in all the costs associated with making that cylinder a functional, working part clamp on a piece of production equipment. Here's what that could look like:

Suddenly, that $100 cylinder is $2,600, which also assumes nobody makes a mistake anywhere in the implementation, uses a rather low burdened labor rate for the calcs, and includes what I believe are actually some pretty aggressive hour estimates. And, like I said above, this isn't even a design that should be implemented 95% of the time because it's generally bad form to use an unsupported cylinder rod to directly act on a part except in very controlled circumstances. Add some bearing supports or a purchased slide, and now you're over $3000.

This of course isn't meant to cause you to shortcut the necessities of a design. It is just to start to build a database of total costs in your head so that you can make the right decisions. Rules of thumb can vary from company to company because of labor rates, efficiencies, levels of standardization, etc, but each company should have a fairly consistent cost of adding certain things. For example, it's been my experience that adding super simple motions like the one above or a gripper, or gag cylinder usually runs $3-4k per. Make it a slide or a bearing supported shaft and cylinder with a little more complicated tooling, you're in the $5-7k range. When it goes up to a profile rail bearing (like THK), custom made saddle, more complex tooling, now you're at the $10-12k range. Make that a servo ballscrew profile rail slide, and it's approaching $18-20k.

In addition to motions, it's also good to have an idea for implemented costs for things like vision systems and robots and hydraulic units so you can make decisions of whether it makes more sense to put together a 3 axis pneumatic slide or buy a small tabletop robot, use a physical probe or buy a camera, choose 4 air/oil intensified cylinders, or much cheaper hydraulic cylinders and a single power unit. I sat in a design review once where a designer designed in a $250 hydraulic cylinder because of the force required. It was the only high force motion on the entire station. To me, it looked like an ideal place for an air/oil intensified cylinder, so I asked him why he chose hydraulics over that. He said (I swear this is true): "The hydraulic cylinder is $250, the air/oil cylinder is $2,500. The cylinder comes out of my budget, but the hydraulic unit (which costs around $8k) comes out of the controls budget." Needless to say, he didn't last long, but the real point of the story is back to the original couple of sentences of this post: you set the course for all other departments (and costs) to follow. There are always multiple ways to accomplish the same thing and as an engineer, you should always be balancing cost with function. Take the time to find or build that simple database of rough numbers early in your career and use it in your thought process and you will make the best decisions possible. Because motions are so expensive, here is the thought process that I tend to go through:

Is it even necessary at all? If I'm talking about a part clamp, what forces at play would make the part jump out of the nest? Can my other tooling have lead ins to guarantee the part location during engagement instead of adding a powered clamp? If adding a motion of any type is for risk mitigation, can I put a hole pattern in the base, but not implement the motion until debug if I run into trouble?
Can I piggyback that motion onto another motion that already exists via a "lost motion" or a cam driven action? This is certainly not meant to be disparaging to controls people (hey, I happen to be one), but as soon as you put a controlled motion into the mix, that's where the real money comes in. Answering this question requires a good feel for risk/reward. A separate motion can be adjusted and moved by itself. It can be re-sequenced via the PLC. You can change its speed. Most of that goes away when you make something purely mechanical, so you have to balance the need with the cost. If it's a low risk part ejector or clamp, making it a cam motion may be a great solution. If it's inserting a high tolerance component, you may want to keep it separate.
How much variability is there? Am I running two different part variants where a pneumatic gag cylinder or simple changeout blocks could be the most cost effective, or am I running 10 variants where I should consider servo motions or robots?
What is the cumulative cost of a solution? Should I go air/oil intensified or hydraulic? Robot or individual motions? Vision or probes?

I hope this is a good starting point for you to start to build an understanding of overall cost of each decision you make. It takes a bit of digging for the info since it's somewhat company specific, but it's worth the effort in the long run.

Please, Never Utter the Phrase "It's Only a $100 Cylinder"